In offshore drilling applications, oilfield tubulars (e.g., casing, drill pipe, strings thereof, etc.) are run from a drilling rig located on a marine vessel or a platform, down to the ocean floor, and then into an earthen bore formed in the ocean floor. In deep-water situations, the time required to run the oilfield tubulars from the drilling rig at the ocean surface to the ocean floor may be significant. Further, drilling equipment, rigs, and drilling services may incur time-based charges during drilling operations, which may be on the order of hundreds of thousands of dollars, or more, per day. Accordingly, such drilling time is at a premium.
One way to conserve time is to run the oilfield tubulars at least partially to the ocean floor during “offline” time. This may be accomplished in a process known as “dual-activity drilling,” whereby casing is run down to, or at least toward, the ocean floor during drilling operations. One way to conduct dual-activity drilling is to use two rotary stations: one primary and one auxiliary. While drilling is being performed in the primary rotary station, the casing string may be run at least partially down to the ocean floor using the auxiliary rotary station. Once deployed to a desired depth, the casing string may be “hung-off” of the drilling rig, i.e., landed in a mobile cart disposed below the auxiliary rotary station, typically in a moonpool. At a desired depth, the drilling operations being performed in the primary rotary station may be stopped, the drill string may be removed, and then the partially-deployed casing string may be moved, e.g., via the cart, to the primary rotary station. The casing string may then be “picked-up” through the primary rotary station, and then deployed into the well using standard casing running equipment.
Typically, such hang-off and pickup operations rely on a “soft-break” process. In the soft-break process, a drill pipe is connected (“made up”) to the top end of the partially-deployed casing string. Although equipment may be available at the rotary station to make this connection at a high torque (e.g., 70,000 ft-lbs or more), a significantly lower torque (e.g., less than the standard, required makeup torque of the connection) is applied to establish connection. The casing string, supported by the stand of drill pipe, is then lowered to the cart, and the weight of the casing string is transferred to the cart.
The drill pipe, which provided the connection to the lifting mechanism used to lower the casing string, is then disconnected (“broken out”) from the casing string to allow the casing string to be moved. Such disconnection may be accomplished using torque available from a top drive, which may be adequate to break-out the lower-torque connection, but would be insufficient to break-out a fully-torqued connection. The cart then moves the casing string into position below the primary rotary station, the drill pipe is again made up to the casing string by another lower-torque connection, e.g., as provided by the top drive, and then casing string is hoisted up through the primary rotary station. Once located at the primary rotary station, any suitable casing running equipment may be employed to run the casing string into the borehole.
In some instances, however, applying less than optimal torque to the connection between the drill pipe and the casing string may result in a connection with compromised strength. If the casing string backs-out or otherwise becomes disconnected during hang-off or pickup, e.g., by failure of such a weakened connection, the casing string may fall to the ocean floor, which may result in a loss of the casing string.
Thus, there is a need for dual-activity capability drilling systems and methods, and apparatus that support the same, which provide or employ secure connections for hang-off and pickup.